The present invention relates to an apparatus and method for producing so called "washed rice".
Most of bran has been removed from surfaces of rice grains called "polished rice" produced by milling or polishing rice grains or kernels by rice polishing machine. A considerable amount of fine bran however still adheres to and remains on surfaces of polished rice. Thus, to produce boiled rice, the polished rice is further washed with water, and is then boiled. Moreover, it is necessary to steep or dip the rice in water for a certain period of time to raise the water content in the polished rice so that the whole region of each rice grain may be uniformly boiled.
The washing of rice with water and steeping or dipping it in water however take considerable time and are laborious. Housewives do not like these operations. In mass production of boiled rice, there is a problem in that a large amount of waste water having used for washing rice is liable to cause pollution of water in addition to the problem of taking rather long time to wash rice and steep it in water. Accordingly, it is strongly desired that rice which may be boiled at once by merely adding water without such washing and steeping operations is supplied.
In this specification (description) and claims, the term "washed rice" is referred, on the hand, broadly to as rice which has been washed with water to such a degree that bran on surfaces of polished rice is substantially removed, and which needs no washing with water before boiling. On the other hand, the term "washed rice" is also referred to, in a narrow sense, as rice which may be boiled at once after water is added without being washed with water or steeped in water. When rice which has been sufficiently polished is sufficiently washed with water, bran is substantially removed from surfaces of the polished rice. Thus, the polished rice washed with water usually does not need steeping in water for a substantial period of time before boiling, and hence washed rice in a broad sense is usually the same as washed rice in a narrow sense.
When polished rice is washed with water, water content thereof increases during washing. Furthermore, water content of polished rice increases if water adheres to or contacts surfaces of polished rice after water-washing thereof. The water content of polished rice is usually 14 to 15% by weight. When the water content becomes beyond 16% by weight, the polished rice is liable to go bad, and it is practically impossible to store it for a long period of time.
Thus, for producing washed rice, both steps of washing the polished rice, and dewatering or removing moisture or water from surfaces of polished rice are indispensable.
Japanese Patent Laid-open (unexamined) Publication No. 1-308779(A) laid open for public inspection on Dec. 13, 1989 discloses a technique in which a rise in water content in the rice grains or kernels is suppressed by washing polished rice with water for a short limited time within 10 seconds and by rapidly dewatering it after washing.
In Japanese Patent Laid-open (unexamined) Publication No. 2-242647(A) laid open on Sept. 27, 1990, there is proposed a technique that steps of water washing and removing water of polished rice are performed for a short time so that the water content of washed rice after the both steps is below 16 weight %.
In this Japanese Patent Laid-open Publication No. 2-242647(A) the "washing rice with water" is defined as washing an amount of rice grains or kernels in such a large amount of water to steep it under water level while agitated or stirred.
Heretofore, continuous rice washing machines in which a great amount of polished rice is washed by stirring it in water have been known (for example, Japanese Patent Laid-open (unexamined) Publication No. 62-282648(A)). It has been also proposed to perform washing of rice, using a rice polisher (Japanese Patent Laid-open Publication No. 1 (1989)-308779(A)).
Other earlier attempts or disclosures are that dewatering is carried out by an air ejection drier (Japanese Patent Laid-open (unexamined) Publication No. 1 (1989)-308779(A), and that a dewatering unit is provided at the outlet of a rotary continuous rice washing machine to continuously conduct dewatering (Japanese Patent Laidopen (unexamined) Publication No. 2 (1990)-242647(A)).
These attempts were, however, mere aggregation of known apparatuses, and the whole equipment for producing washed rice by continuously performing washing and dewatering of polished rice rather increases in size and hence in stallation space.
The inventors have proposed a washed rice producing apparatus including two rice washing units, a dewatering unit and a drying unit in Japanese Patent Application No. 1 (1989)-244499, which was substantially kept secret and was not laid open to public as of Dec. 18, 1990. Also, in this washed rice producing apparatus, such a problem of increasing in size of the whole apparatus remains unsolved.